Apparatus for displaying graphics symbols

• US 4,297,693 A
• Filed: 02/02/1979
• Issued: 10/27/1981
• Est. Priority Date: 06/21/1976
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Parsons, Robert
• Primary Examiner(s): Curtis, Marshall M.
• Application Number:
  US06/008,722
• Time in Patent Office: 998 Days
• Field of Search: 340/747, 340/751, 340/790, 340/744, 340/732, 340/750, 340/799, 340/721, 340/801
• US Class Current: 345/24
• CPC Class Codes: G09G 5/222 Control of the character-code memory

Abstract

Apparatus suitable for use with teletext display apparatus which is arranged to operate in a plurality of display modes, including a graphic display mode, in response to digital coded control signals, and to display in each mode digital coded data signals which provide the display information for the viewer. The digital coded control signals are interspersed among the digital coded data signals, with the result that no display information is normally available when a digital coded control signal is present, but the apparatus is so arranged that, in the graphics display mode, the digital coded, data signal which arrived immediately before the digital coded control signal is held over, and used to fill in the blank space that would correspond to the presence of the digital coded control signal. `Hold over` is effected by arranging that a current data signal is held in a data store, and that the stored data is pushed out only by a subsequent data signal.

Claims

1. Apparatus for controlling the display of information which is built up line by line on a raster-type display in response to digital coded data and mode control signals selectively occurring during individual lines of said display, there being a plurality of modes including a graphics mode in which data signals can be displayed during a respective line of said display, the mode control signals indicating the mode in which subsequent data signals are to be displayed during at least part of that line but not themselves generating a display, the apparatus including graphics symbol store means for providing in the graphics mode, in parallel, signals representative of the specified graphics symbol until a further data signal is received, parallel to serial converter means for securing the parallel signals from the graphics symbol store means and in response thereto producing in serial form, signals characteristic of the graphics symbol to be displayed, and control logic means for changing the contents of the graphics symbol store means in response to a graphics symbol signal and to cause said store means to continue to produce the parallel signals already stored in the graphics symbol store means for the duration of a mode control signal when the said mode control signal occurs in place of a data signal during the display of graphics symbols and thereby avoid a blank space in said display resulting from occurrence of said mode control signal.

2. Apparatus as claimed in claim 1, wherein the graphics symbol store means includes a graphics symbol generator which is arranged to generate a two-bit code which is representative of the graphics symbol to be displayed, and left and right 1-bit data stores which are arranged to receive the said two-bit code and to store it until the next graphics symbol signal is received.

3. Apparatus as claimed in claim 2, wherein the parallel to serial converter means includes a parallel to serial shift register and control logic means for said shift register connected for receiving said two-bit data and in response thereto to output a corresponding seven-bit parallel input to said shift register.

4. Apparatus as claimed in claim 1, wherein the graphics symbol store means is so arranged that data signals which are subsequent to a graphics mode control signal can overwrite the data stored in the graphics symbol store means, and a subsequent mode control signal is prevented from overwriting the data stored in the graphics symbol store means.

5. In line scan raster-type display apparatus which is arranged to display digital coded data signals in a plurality of display modes which correspond to a plurality of digital coded mode control signals each of which, in operation, appears during a line scan in place of a digital coded data signal, the display mode including a graphics symbol mode, the improvement comprising a graphics symbol store which is arranged to provide in the graphics mode, in parallel, signals representative of the graphics symbol specified by the current digital coded data signal until a further data signal is received, a parallel to serial converter which is arranged to receive the parallel signals from the graphics symbol store and to provide, in serial form, signals appropriate to the graphics symbol to be displayed, and control logic means for changing the contents of the graphics symbol store only in response to a graphics symbol signal so that the contents of the graphics symbol store are displayed as a graphics symbol for the duration of any digital mode control signal which appears in place of a digital coded data signal in a line scan during the display of graphics symbol, thereby avoiding a blank display during occurrence of the said mode control signal.

6. Display apparatus as claimed in claim 5, wherein the graphics symbol includes graphics symbol generator means for generating a two-bit code which is representative of the graphics symbol to be displayed, and left and right 1-bit data stores which are arranged to receive the said two-bit code and to store it until the next graphics symbol signal is received.

7. Display apparatus as claimed in claim 6, where the parallel to serial converter includes a parallel to serial shift register and its associated control logic which is arranged to receive the two-bit data from the graphics symbol store and to provide seven-bit data from the said two-bit data.

8. Display apparatus as claimed in claim 5, wherein the graphics symbol store is so arranged that data signals which are subsequent to a graphics mode control signal can overwrite the data stored in the graphics symbol store, and a subsequent control signal is prevented from overwriting the data stored in the graphics symbol store.

9. Display apparatus as claimed in claim 7, wherein the parallel to serial shift register control logic is arranged to modify the seven-bit data in accordance with data signals subsequent ot a non-graphics mode control signal.

10. Apparatus for controlling the display of information by a line scan raster-type display in response to digital coded data and mode control signals selectively occurring during individual lines of said display, there being a plurality of modes including a graphic mode in which data signals can be displayed during a respective line of said display, said mode control signals indicating the mode in which subsequent data signals are to be displayed during at least part of that line but not themselves generating a display, comprising:

11. random access memory means storing at least said graphics symbol signal data and mode control data;

graphics symbol generator means operably connected to said random access memory means for selectively receiving therefrom individual graphics symbol signal data and mode control data and to generate in response to an item of graphics symbol data a two-bit coded output representative of that particular graphics symbol until a further item of signal data is received from said random access memory means;

first and second one-bit data stores for receiving and storing said two-bit coded output from said graphics symbol store means;

parallel to serial converter means including a parallel to serial shift register means and control logic means for said shift register means connected for receiving said two-bit coded output from said graphics symbol generator means and in response thereto to produce and input a corresponding seven-bit parallel input to said shift register means for producing a serial output from said shift register means characteristic of the particular graphics symbol to be displayed;

and logic means for changing the contents of said one-bit stores only in response to receipt of a further item of graphics symbol signal data by said graphics symbol generator means and for inhibiting the change of the contents of said one-bit stores in response to a subsequently occurring item of mode control data thereby to cause said shift register means to continue to produce said serial output corresponding to said particular graphics symbol for display for the duration of said mode control data.